This application relates to optical resonators and cavities, and more specifically, to optical whispering-gallery-mode (“WGM”) resonators and cavities.
A dielectric material may be shaped to form an optical whispering-gallery-mode (“WGM”) resonator which supports a special set of resonator modes known as whispering gallery (“WG”) modes. These modes represent optical fields confined in an interior region close to the surface of the resonator due to the total internal reflection at the boundary. Microspheres with diameters from few tens of microns to several hundreds of microns have been used to form compact optical WGM resonators. Such spherical resonators include at least a portion of the sphere that comprises the sphere's equator. The resonator dimension is generally much larger than the wavelength of light so that the optical loss due to the finite curvature of the resonators is small. As a result, a high quality factor, Q, may be achieved in such resonators. Some microspheres with sub-millimeter dimensions have been demonstrated to exhibit very high quality factors for light waves, ranging from 1000 to 109 for quartz microspheres. Hence, optical energy, once coupled into a whispering gallery mode, can circulate within the WGM resonator with a long photon life time.
Such high Q values are generally difficult and expensive to obtain in conventional Fabry-Perot optical resonators formed is with mirrors. The capability of producing high Q values makes the WGM resonators useful for many optical applications, including optical filtering, optical delay, optical sensing, lasers, and opto-electronic oscillators.